Tape-springs are known as such in the space domain as being tapes that can switch from the wound state to the unwound state essentially by virtue of their own elastic energy; in the unwound state, the known tape-springs generally exhibit a rigidity capable of maintaining them in that state.
The conventional tape-springs, generally metallic, therefore have a natural tendency to unfold to be in their stable state. If they are forced to fold up, they have a tendency to form a radius equal to that of their transversal radius of curvature. It therefore requires a weak external force to keep them wound in this form. If this force is abruptly eliminated, the unfolding can be violent and uncontrolled, that is to say that the whole tape-spring may have a tendency to straighten up simultaneously, over its entire length. The conventional tape-springs may thus offer difficulties in terms of controlling their unfolding.
Conventional tape-springs made of composite material have also been developed. The latter have properties that are for the most part similar to those of the conventional metal tape-springs, but offer the advantage of making it possible, to a certain extent, to control their own winding radius. They also offer the advantage of a high rigidity/weight ratio and a low expansion coefficient.
The applicant has already demonstrated that it is possible to associate a conventional tape-spring with a layer of thermoplastic material. This invention was the subject of the patent application FR 0803986. The conventional tape-spring comprising a layer of thermoplastic material can be wound by force, heated then cooled such that the thermoplastic fixes the tape-spring in the wound state, which then becomes the stable state. By locally heating, it is possible to progressively unwind the assembly.
Alternatively, it is possible to use, instead of the thermoplastic material, a thermosetting material or, more generally, a material exhibiting a strong rigidity variation on crossing a temperature threshold.
Finally, by construction, it is possible to render a composite tape-spring bistable. Studies have been published on this issue, such as, notably, “Carbon Fibre Reinforced Plastic Tape-springs”, J. C. H. Yee et al., AIAA 2004-1819, and “Analytical models for bistable cylindrical shells”, S. D. Guest et al.
The remarkable property of the bistable tape-springs lies in the fact that they are mechanically stable both in the unwound state and in the wound state. The more stable state does, however, remain the unwound state. The bistable tape-springs are wound via a generally great force. They remain stable in the wound state around their natural radius of curvature, with no external force. All that is required is to unfold one end thereof, with a force of low intensity, exerted by a motor-driven system, for example, to initiate the unwinding. The unwinding can be very fast, but remains progressive from the initial unwinding point.
In this context, the general issue to be addressed lies in the deployment of very large sized solar generators and how to deploy a three-dimensional reinforcing structure to support solar generators having a very large surface area.
The prior art does not propose any satisfactory technological solution and the present invention seeks to fill this gap.